The present invention relates to an image processing apparatus and an image processing method.
Conventionally, an image processing apparatus such as, for example, a color copying machine executes a color printing process on the basis of a color image signal from a color sensor, and when monochrome printing is desired or copy of a monochrome original document is executed, it converts the color image signal from the color sensor into a monochrome image signal and executes a monochrome printing process on the basis of the monochrome image signal. Then, for determination between color and monochrome, there are adopted methods for determining by once storing the color image signal in a memory, by pre-scanning, and the like.
Moreover, there is generally executed a method in which, when the color image signal is stored in the memory, the color image signal is compressed after being converted from a luminance-system signal into a color-difference-system signal so as to be stored in the memory.
That is, for example, Japanese Patent No. 2755972 discloses a technique relating to a color image processing apparatus determines whether the color image signal from the color sensors of RGB is color or monochrome every pixel, and as a result, when it is monochrome, processes the monochrome pixels as the monochrome image signals by using only the image signal of G, so that the apparatus generates a good monochrome image signal by preventing a sensor error, which is an inconvenience of the color sensor, from occurring.
However, although this technique can generate a good image by preventing the sensor error from occurring concerning monochrome characters being color-processed and the like, when the monochrome process is desired for all pixels, there has been a possibility that the picture quality of the original document with poor sensitivity of a G signal such as one with a red stamp or one written by a blue ball-point pen deteriorates since the technique generates the monochrome image signal by using only the image signal of G.
Moreover, Japanese Patent No. 2720924 discloses a technique relating to a coding apparatus for the image signal that stores the color image signal from the color sensor in the memory after converting it from the luminance-system signal into the color-difference-system signal, and it outputs either a color-compressed result or a monochrome-binary-compressed result to a transmission path in accordance with the result of the determination between a predetermined color or monochrome.
However, there has been a possibility that the picture quality deteriorates during monochrome output since the technique stores only the color image signal from the color sensor in the memory.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. 5-153405 discloses a technique that executes efficient coding by implementing blocking of the image on the basis of a luminance signal and a sub-sampled color difference signal and by extracting an outline from a luminance component in the block unit.
However, there has been a problem that a required capacity of the memory increases since execution of sampling concerning the color difference is necessary in this technique.